Article of aluminum-base alloy



United States Patent Deiaware No Drawing. Filed Nov. 27, 1961, Ser. No.155,165 5 Claims. (Cl. 75-1225) The invention relates to die-expressedarticles of aluminum-based alloy. It more particularly concerns animproved method of producing die-expressed articles ofdispersion-hardened aluminum-base alloys whereby good mechanicalproperties are attained which are not appreciably lowered by exposure toelevated temperatures.

This application is a continuation-impart of a priorfiled application,Serial No. 810,258, filed May 1, 1959, now abandoned.

Heretofore high strength aluminum-base alloys have been prepared byalloying aluminum with one or more suitable constituents which arecapable of forming solid solutions with aluminum. Such alloys are oftenfurther treated, as by solution and precipitation, heat treating andcold-working, to increase yield and tensile strength. However, atelevated temperatures the eiiectiveness of solid solution strengtheningand precipitation hardening is limited and further the benefits ofcold-working and aging are soon lost because recovery, recrystallizationand overaging take place upon heating the alloys to even rather moderatetemperatures. In other attempts to produce high strength aluminum-basealloys, fine aluminum powder having a thin oxide coating has beendie-expressed to produce an extrude in which aluminum oxideis widely andfinely dispersed in an aluminum metal matrix. While so-tormed extrudesexhibit good mechanical properties, they tend to be quite brittle anddifiicult to form even at elevated temperatures. In addition, extremelyfine aluminum powder is required to provide sufliciently wide dispersionof the oxide in the extrude as the oxide is present only as a surfacecoating on the so-particulated metal particles. The preparation ofaluminum powder of sulficient fineness is not only expensive but thefine powder is hazardous to handle.

It is therefore an object of the invention to provide an improved methodof forming an aluminum-base alloy having superior physical andmechanical properties at elevated temperatures. A further object is toprovide an improved method of preparing an aluminum-base alloy which hassuperior mechanical and physical properties but is still readilyformable into useful shapes.

A still further object of the invention is to provide an improvedaluminum-base alloy having superior mechanical and physical propertieswhich are not appreciably decreased by exposure to elevatedtemperatures.

These and other objects and advantages of the invention will bemorefully understood on becoming familiar with the following description andthe appended claims.

This invention is predicated on the discovery that, by preparing analuminum-base alloy containing aluminum and one or more constituentswhich are each miscible with aluminum in the molten state butsubstantially insoluble in solidified aluminum and by rapidsolidification of said alloy, for example, into a mass of atomizedparticles, heating, compacting and then die-expressing the solidifiedmetal to form an extrude or die-expressed article, the so-obtainedarticle exhibits exceptionally desirable mechanical properties; Forpurposes of the specification and claims the term solidified aluminum isextended in meaning to include solidified aluminum-base alloy.

In carrying out the invention, an aluminum-base alloy containing atleast 70 percent of aluminum is prepared by alloying, according to wellknown methods, aluminum and one or more constituent metals having thehereinafter defined specific properties. An essential constituent metalmust have suflicient solubility in molten aluminum at reasonablealloying temperatures, for example 650 to 900 C., to avoid the necessityof employing high temperatures at which aluminum readily attackscontainer materials, but a solid solubility in aluminum andaluminum-base alloy of less than 0.1 atomic percent. The use of metals,such as boron, which exhibit the requisite low solid solubility insolidified aluminum but which are difiicult to alloy in effective amountin molten aluminum is undesirable in the practice of the invention. Asto the solid solubility in aluminum, those elements which on coolingform an intermetallic compound with aluminum, and which are insoluble insolid aluminum are employed. The insoluble phase must remain suspendedin the rapidly cooled and solidified aluminum. It is further desirablethat the molten alloy exhibit a narrow solidification range so that sizeof the intermetallic compound particles is minimized. It is desired thatthe intermetallic particles dispersed in the solid aluminum have amaximum diameter of about 0.0001 inch or less, preferably'as small asabout 0.00005 inch or less since the smaller the particle size the morethe improvement in properties that results. A few particles havinglarger diameters can be tolerated but they should be kept to a minimumto avoid adversely affecting the properties of the final product.Suitable metal constituents that may be used singly or in combination inthe practice of the invention include gold, barium, rare earth metals,palladium, platinum, antimony, selenium, strontium, tellurium, thoriumand uranium, the pertinent propertles of wh1ch are listed m Table I.

TABLE I Wt. percent Liquid of constit- Solid solubility Solidusl'nteruent to Metal solubility in A1 at temperametallic form 10%constituent inAl, Wt. 800 0., ture of A] compound by volume percent Wt.Binary, formed of interpereent C. with Al metallic compound (estimated)1 30 642 AuAlz 20 nil 10 652 BaAl4 10 0. 05 20 638 CeA14 l0 nil 50 615PdAl3 8 nil 40 639 PtA]a 12 0. 1 10 057 SbAl l. 18 nil 22 648 SeaAl-z 15nil nil 53 621 20 0. 01 30 632 18 nil 20 640 15 1 Similar to barium.

The alloy to be used is brought to the molten state in any convenientmanner in preparation for rapid solidification. Temperatures in theorder of 25 to 50 centigrade degrees above the melting point of thealloy are desirable although other temperatures may be used at which thealloy is in the molten state. It is preferable to use the lowertemperature of a molten state not only so as to reduce the degree ofhazard involved in handling the molten alloy but also to reduce theamount of heat which must be removed to permit the molten alloy toreturn to the solid state. It is highly desirable for reasonshereinafter more fully discussed that the solidification of the atomizedalloy take place quickly in order to minimize aggregation or crystalgrowth of intermetallic compounds which are insoluble in solidifiedaluminum.

The alloy while in the molten state may be subjected to a dispersion andchilling operation whereby the metal is obtained in atomized form, thatis, in the form of fine individually frozen discrete pellets. There arevarious ways in which atomization may be performed and any one of themmay be used. A convenient method appears to be directing a jet of aninert cooling gas against an unconfined stream of the molten alloy asdescribed in U.S. Patent No. 2,630,623.

For example, a freely falling stream of the molten metal may be brokeninto droplets and solidified by impinging upon the stream an inert gassuch as a hydrocarbon gas (e.g., methane, ethane, propane, butane,etc.), argon, helium, hydrogen, the inert gas having a boilingtemperature below the melting point of the molten metal. A wide range ofpellet sizes, although small, usually results from the atomizingoperation. The atomized product comprises more or less spherical pelletsfor the most part ranging in size from about mesh to smaller than 325mesh. A preferred range of pellet sizes is from about 325 mesh to about140 mesh because of the outstanding properties achieved. However, verygood properties are achieved with pellet sizes predominating in the 30to 60 mesh range.

These pellets exhibit very desirable mechanical properties and may beused as pellets, per se, for example, to reinforce other metals, as aload support, etc. or may be further fabricated, as by extrusion,rolling, and the like.

Of course, other methods of rapidly quenching appropriate alloycompositions, as well as other methods of atomizing aluminum may beemployed.

As a result of the atomizing operation, there is imparted to each pelletof the aluminum-base alloy a special heterogeneous microstructureessential in achieving the objects of this invention. This structure ischaracterized The amount of reduction in the cross-sectional dimensionsof the compact effected by the extrusion or dieexpression is subject towide variations and may be from about 5 to 1 to as much as 200 to l ormore (i.e., from about 80 percent to over 99 percent reduction incrosssectional area).

The so-produced extrude having a uniform dispersion of finely-dividedintermetallic compounds exhibits enhanced properties at both room andelevated temperatures and is less adversely affected by fabrication orheat treatment at high temperatures.

Example In accordance with the invention, a quantity of each of thealuminum-base alloys listed in Table II in atomized form was provided.In each instance, the atomized pellets contained a uniform dispersion ofintermetallic compound in which the intermetallic compound had anaverage diameter of about 0.00005 inch, substantially none of theintermetallic compound having a diameter greater than 0.0001 inch. Ineach case the quantity of atomized material was charged into acylindrical container 3 inches in internal diameter, the container beingat 400 C. The charge had a depth of about 6 inches and was compacted at400 C. in the container to a compact about 4 inches long. The compactwas then die-expressed at the same temperature at the rate of 5 feet perminute into a strip having a rectangular cross section 1 /4 inches by/1t; inch, tie reduction in area being about 90:1. The so-obtaineddie-expressed articles were subjected to physical testing at 24 C., 315C. and 427 C. The results of the tests are listed in Table II.

TABLE II Composition Properties at 24 0. Properties at Properties at RunNo.

Per- Per- Per- Per- Per- Per- Percent cent cent cent cent TYS CYS TScent TYS TS cent TYS TS Th Ba MM Al E E E MM=Misch Metal.

by an aluminum metal matrix having uniformly dispersed therethrough adiscontinuous phase made up of very fine crystallites of anintermetallic compound thereof with aluminum. The intermetallic compoundis present in an amount totaling by volume from about 0.5 to 20 percentof the alloy and preferably from 3 to 15 percent.

In the next step of the method, the rapidly solidified metal is heatedin preparation for compacting and dieexpression. Compacting anddie-expression may be carried out in conventional apparatus designed forthe extrusion of aluminum-base alloy. A suitable method and apparatusfor carrying out the die-expression of pelletized light metal, such asaluminum, is described in US. Patent No. 2,630,623. The temperature towhich the metal is heated is within the conventional plastic deformationtemperature range for aluminum-base alloys, usually between about 250 C.and 500 C. but always below that tempcrtaure which affects thedispersion through agglomeration. A preferred range is about 315 to 427C.

It has been found that the as-atomized aluminum-base alloy may be heatedin bulk to the desired temperature merely by placing it in a suitablemetal vessel in a heated oven. Or, it is possible to charge the heatedcontainer of a die-expressing apparatus with as-atomized metal andproceed with the operation of the apparatus to efiect die-expressionwith substantially no destruction of the as-atomized microstructure ofthe alloy.

In another embodiment of the invention, an aluminumbase alloy isprepared by making suitable additions to aluminum of a metalconstituent, which forms an insoluble phase therewith as describedhereinabove as well as one or more metals which increase the strength ofaluminum in a well known conventional manner such as by solutionhardening. It has thus been found that the benefits of dispersionhardening may be combined with the benefits of increasing the strengthof the matrix about the finely dispersed crystallites of solid insolublephase. Metals which may be added variously to increase the matrixstrength include:

Weight percent Use of combinations of the above-listed elements inamount in which the metals are incompatible by virtue of mutualinsolubility in molten aluminum whereby a precipitate is formed whichsettles from the melt, or in amounts which otherwise fail to increasematrix strength, is of no advantage in the practice of the invention.While simple binary or ternary combinations of the above-listed matrixstrengthening constituents are believed to be compatible, it is withinthe skill of the metallurgist to check desired alloying combinations forincompatibility such as insolubility in molten aluminum. In general, anyconventional aluminum-base alloy system may be employed, such as AlMg,AlCu, AlMn, AlSi, Al-Zn, Al--MgZn, or AlSiCu, in combination with one ormore of the previously mentioned metals which form a solid insolublephase in solidified aluminum.

Such composite alloys, that is, those including dispersion hardening, asWell as conventional strengthening alloying metals, are atomized,compacted, and extruded as described hereinabove.

Various modifications may be made in the present invention Withoutdeparting from the spirit or scope thereof and it is to be understoodthat I limit myself only as defined in the appended claims.

What is claimed is:

1. Atomized pellets comprising from 0.5 to 20% by volume of particles ofsolid insoluble aluminum intermetallic compound and the balancealuminum-base alloy; said particles having maximum diameters of 0.0001inch and being intimately and uniformly dispersed throughout saidaluminum-base alloy; said aluminum intermetallic compound being selectedfrom the group consisting of AuAlz, BaAl CeAl PdA1 PtA13, Se Al SI'A14,TeAl ThAl UAl and mixtures thereof; said atomized pellets comprising atleast about 70% of aluminum; and said atomized pellets having diameterssmaller than about mesh.

2. Atomized pellets comprising from 3 to by volume of particles of solidinsoluble aluminum intermetallic compound and the balance aluminum-basealloy; said particles having maximum diameters of 0.0001 inch and beingintimately and uniformly dispersed throughout said aluminum-base alloy;said aluminum intermetallic compound being selected from the groupconsisting of AuAl BaAl CeAl PdAl PtAl SbAl, Se Al SrAl TeAl 6 ThAl UAL,and mixtures thereof; said atomized pellets comprising at least about ofaluminum; and said atomized pellets having diameters smaller than about10 mesh.

3. Atomized pellets consisting essentially of from 0.5 to 20% by volumeof particles of solid insoluble aluminum intermetallic compound, and thebalance aluminumbase alloy containing at least one matrix strengtheningalloying constituent selected from the group consisting of silver,calcium, chromium, copper, lithium, magnesium, manganese, silicon,titanium, zinc; said particles having maximum diameters of 0.0001 inchand being intimately and uniformly dispersed throughout saidaluminum-base alloy; said aluminum intermetallic compound being selectedfrom the group consisting of AuAl BaAl CeAl PdAl PtAl SbAl, Se Al SrAlTeAl ThAl UAl and mixtures thereof; said atomized pellets comprising atleast about 70% of aluminum; and said atomized pellets having diameterssmaller than about 10 mesh.

4. Atomized pellets consisting essentially of from 0.5 to 20% by volumeof solid insoluble ThAl particles and the balance aluminum-base alloy;said ThAl particles having maximum diameters of 0.0001 inch and beingintimately and uniformly dispersed throughout said aluminum-base alloy;said atomized pellets comprising at least about 70% of aluminum; andsaid atomized pellets having diameters smaller than about 10 mesh.

5. Atomized pellets of aluminum-base alloy comprising at least about 70%aluminum and from 0.5 to 20% by volume of solid insoluble AuAl particlesintimately and uniformly dispersed throughout said aluminum, said AuAlparticles having a maximum diameter of 0.0001 inch, said atomizedpellets having diameters smaller than about 10 mesh.

References Cited in the file of this patent UNITED STATES PATENTS2,056,604 Guertler Oct. 6, 1936 2,087,269 Stroup July 20, 1937 2,659,131Leontis et al Nov. 19, 1953 2,950,188 Picklesimer et a1. Aug. 23, 19602,966,736 Towner et al. Jan. 3, 1961

1. ATOMIZED PELLETS COMPRISING FROM 0.5 TO 20% BY VOLUME OF PARTICLES OFSOLID INSOLUBLE ALUMINUM INTERMETALLIC COMPOUND AND THE BALANCEALUMINUM-BASE ALLOY; SAID PARTICLES HAVING MAXIMUM DIAMETERS OF 0.0001INCH AND BEING INTIMELY AND UNIFORMLY DISPERSED THROUGHOUT SAIDALUMINUM-BASE ALLOY; SAID ALUMINUM INTERMETALLIC COMPOUND BEING SELECTEDFROM THE GROUP CONSISTING OF AUAL2, BAA,4, CEAL4, PDAL3, PTAL3, SBAL,SE3AL2, SRAL4, TEAL3, THAL3, UAL4 AND MIXTURES THEREOF; SAID ATOMIZEDPELLETS COMPRISING AT LEST ABOUT 70% OF ALUMINUM; AND SAID ATOMIZEDPELLETS HAVING DIAMETERS SMALLER THAN ABOUT 10 MESH.